Method for preparing semiconductor substrate with insulating buried layer by gettering process

ABSTRACT

A method for preparing a semiconductor substrate with an buried insulating layer by a guttering process, includes the following steps: providing a device substrate and a supporting substrate; forming an insulating layer on a surface of the device substrate; performing a heating treatment on the device substrate, so as to form a denuded zone on the surface of the device substrate; bonding the device substrate having the insulating layer with the supporting substrate, such that the insulating layer is sandwiched between the device substrate and the supporting substrate; annealing and reinforcing a bonding interface, such that an adherence level of the bonding interface meets requirements in the following chamfering grinding, thinning and polishing processes; performing the chamfering grinding, thinning and polishing processes on the device substrate which is bonded.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method for preparingsilicon-on-insulator (SOI) material, and more particularly to a methodfor preparing a semiconductor substrate with an insulating buried layerby a gettering process.

2. Description of Prior Art

With miniaturization of feature sizes of integrated circuits, it isimportant to control defects in single crystal silicon. The defects insilicon wafers mainly come from two aspects. In one aspect, grow-indefects, such as crystal originated particles (COPs), are producedduring crystal growth processes. In the other aspect, defects areproduced when performing heating treatments on the silicon wafers, suchas oxygen precipitation. If these defects are positioned in activeregions on surfaces of the silicon wafers, performance of devices isdeteriorated and the devices are failed. Furthermore, when the siliconwafers are processed and the integrated circuits are manufactured, theyare inevitable to be polluted by metals, such as Cu, Ni, Fe and so on.These metal impurities diffuse fast in the silicon. If the metalimpurities exist in the active regions of the devices, the devices arefailed. Accordingly, it is quite important to effectively remove themetal impurities on the surfaces of the silicon wafers. The oxygenprecipitation and induced defects thereof may be served as getteringpoints for gettering the metal impurities, such that the metalimpurities are collected in the defects. But if the oxygen precipitationand the induced defects occur in the active regions of the devices,electrical performances of the devices are affected as well.Accordingly, on the one hand, the oxygen precipitation is required to beproduced in the silicon wafers for achieving a gettering function indevice technology, but on the other hand, it is hoped that the oxygenprecipitation does not occur in the active regions of the siliconwafers. These are basic ideas of internal gettering. In the internalgettering technology of the silicon wafers, denuded zones (DZ) with lowoxygen and low metal are formed on the surfaces of the silicon wafers bythe heating treatments, and the oxygen precipitation and the induceddefects are formed inside the silicon wafers for gettering the metalimpurities. After the DZ technology processes are performed on thesilicon wafers, the devices are prepared in the DZ and yields of thedevices may be effectively increased.

Furthermore, thick-film SOI materials (a top silicon layer is usuallygreater than 1 μm) are widely applied to high-voltage power devices andmicroelectromechanical system (MEMS) fields and have rapid developmentespecially in automotive electronics, displays and wirelesscommunications. Since control and conversion of power, automotiveelectronics and power consuming devices have high requirements for harshenvironment, high temperature, high current and high power, the SOIdevices must be utilized based on strict requirements of reliability.Currently, users of the thick-film SOI materials mainly comprise MaximUSA, ADI, TI (USA), NEC Japan, Toshiba, Panasonic, Denso, TI (Japan),FUJI, Omron, Philips European and X-Fab. Among the users of thethick-film SOI materials, a lot of applications mainly come from drivingcircuits in the applications. For instance, the main applications ofMaxim are amplifying circuits in mobile receivers, The main applicationsof Panasonic, TI, FUJI, Toshiba and NEC are scan driving circuits indisplay driving circuits. The applications of DENSO are automotiveelectronics and wireless radio frequency circuits. The applications ofToshiba are power control circuits in air conditionings. Theapplications of Omron mainly comprise sensors. The applications of ADImainly comprise high-temperature circuits and sensors. The applicationsof Phillips mainly comprise LDMOS in power devices for consumingelectronics, such as car stereos and audio amplifiers. The applicationsof Magnchip (Hynix) in Korea comprise display driving circuits indigital cameras produced for Kopin and display driving circuits in PDPsproduced for LG.

However, since a buried oxide layer exists in the SOI material exists,oxygen elements are externally diffused after the heating treatments andthe oxygen elements in the top silicon layer are increased. Accordingly,traditional gettering processes are not suitable for the SOI materials,and the DZ regions do not exist in the top silicon layer, such that thedevice yields by utilizing the SOI materials are relatively low.

SUMMARY OF THE INVENTION

A technical problem solved by the present invention is to provide amethod for preparing a semiconductor substrate with a buried insulatinglayer by a gettering process.

To solve the above-mentioned problem, the present invention provides amethod for preparing a semiconductor substrate with a buried insulatinglayer by a gettering process, which comprises the following steps of:providing a device substrate and a supporting substrate; forming aninsulating layer on a surface of the device substrate; performing aheating treatment on the device substrate, so as to form a denuded zoneon the surface of the device substrate; bonding the device substratehaving the insulating layer with the supporting substrate, such that theinsulating layer is sandwiched between the device substrate and thesupporting substrate; annealing and reinforcing a bonding interface,such that an adherence level of the bonding interface meets requirementsin the following chamfering grinding, thinning and polishing processes;and performing the chamfering grinding, thinning and polishing processeson the device substrate which is bonded.

In one preferred technical scheme, the device substrate is a singlecrystal silicon substrate.

In one preferred technical scheme, the method further comprises thefollowing steps of: performing an additional annealing and reinforcingprocess on the bonding interface after performing the chamferinggrinding, thinning and polishing processes on the device substrate.

In one preferred technical scheme, the step of performing the heatingtreatment on the device substrate further comprises: a first heatingtreatment step for forming a crystal zone on the surface of the devicesubstrate; and a second heating treatment step in which a temperature islower than a temperature in the first heating treatment step, such thatnucleation of saturated oxygen elements outside the denuded zone of thedevice substrate occurs.

In one preferred technical scheme, the step of performing the heatingtreatment on the device substrate further comprises: a third heatingtreatment step for making the nucleation of the oxygen elements in thesecond heating treatment step form a larger oxygen precipitation, andmeanwhile the oxygen precipitation can getter metal impurities in thedenuded zone.

In one preferred technical scheme, the method further comprises thefollowing steps of: forming a protective layer on an exposed surface ofthe supporting substrate before performing the chamfering grinding,thinning and polishing processes on the device substrate.

An advantage of the present invention is that the gettering process isperformed on the device substrate before bonding. The denuded zone isformed on the surface, and then the denuded zone is transferred to thesupporting substrate for obtaining bonding material with high crystalquality. For further consideration of thermal stability of the oxygenprecipitation inside the device substrate, two steps of annealingprocesses may be chosen to be implemented in the preparing process. Thefirst annealing step is a low-temperature annealing, such that thebonding strength meets the requirements in the grinding and polishingprocesses, Finally, the second step is utilized for reinforcing thebonding strength for forming covalent bonds in the interface.

Furthermore, in the heating treatment process, only the first and secondheating treatment steps are performed on the device substrate, and thethird high-temperature heating treatment step and the subsequent step ofreinforcing the bonding interface are integrated as one step, therebyreducing the process complexity, saving the process cost and increasingthe process efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of implementation processes of the present method;and

FIG. 2A to FIG. 2E are schematic diagrams of processes in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A method for preparing a semiconductor substrate with a buried insultinglayer by a gettering process in accordance with an embodiment of thepresent invention is described with referring to appended figures.

FIG. 1 is a flowchart of implementation processes of the present method,which comprises: Step S10, providing a device substrate and a supportingsubstrate; Step S11, forming an insulating layer on a surface of thedevice substrate; Step S12, performing a heating treatment on the devicesubstrate, so as to form a denuded zone on the surface of the devicesubstrate; Step S13, bonding the device substrate having the insulatinglayer with the supporting substrate, such that the insulating layer issandwiched between the device substrate and the supporting substrate;Step S14, annealing and reinforcing a bonding interface, such that anadherence level of the bonding interface meets requirements in thefollowing chamfering grinding, thinning and polishing processes; StepS15, performing the chamfering grinding, thinning and polishingprocesses on the device substrate which is bonded; Step S16, performingan additional annealing and reinforcing process on the boding interface.

FIG. 2A to FIG. 2E are schematic diagrams of processes in accordancewith an embodiment of the present invention.

Referring to step S10 as shown in FIG. 2A, a device substrate 100 and asupporting substrate 190 are provided. The device substrate 100 isutilized for forming a device layer of a final product, and thusmaterial thereof should be a common semiconductor material, such assingle crystal silicon or other compound semiconductor. The supportingsubstrate 190 only has a supporting function, and thus materialselection thereof has a wide range. In addition to the single crystalsilicon or other compound semiconductor, sapphire or a metal substratemay be utilized. In the present embodiment, both of the device substrate100 and the supporting substrate 190 are made of single crystal silicon.

Referring to Step S11 as shown in FIG. 2B, an insulating layer 110 isformed on a surface of the device substrate 100. The insulating layer110 is utilized for forming a buried insulating layer of the finalproduct, and material thereof may be silicon oxide, silicon nitride andso on. A growth method may be a chemical vapor deposition or thermaloxidation (utilized for forming a silicon oxide insulating layer on thesurface of the single crystal silicon substrate).

Referring to Step S12 as shown in FIG. 2C, a heating treatment isperformed on the device substrate 100, so as to form a denuded zone 101on the surface of the device substrate 100.

The above-mentioned step may be further divided into three heatingtreatment steps comprising a heat-up step, a cool-down step and aheat-up step. In a first heating treatment step, a crystal zone isformed on the surface of the device substrate 100. In a second heatingtreatment step, a temperature is lower than that in the first heatingtreatment annealing step, such that a nucleation of saturated oxygenelements outside the denuded zone of the device substrate occurs. In athird heating treatment step, a larger oxygen precipitation is formedfrom the nucleation of the oxygen elements in the second heatingtreatment step, and meanwhile the oxygen precipitation can getter metalimpurities in the denuded zone.

Specifically, the first heating treatment step is a heat-up step. Atarget temperature is one temperature in a range of 900° C.-1400° C. Apreferred target temperature is 1250° C. After the target temperature isreached, an annealing time lasts for 0.5-20 hours. A preferred annealingtime is 4 hours. A heat-up rate is 0.5-20° C./minute. A preferredheat-up rate is 3° C./minute. A preferred protective atmosphere duringthe heat-up process is Ar/O₂ mixture, other gas or other gas mixture. Anannealing atmosphere may be one of N₂, Ar (or other inert gas), H₂, O₂,N₂/O₂ mixture, Ar/O₂ mixture, Ar/H₂ mixture and N₂/Ar mixture. In thefirst heat-up and annealing process, an out diffusion of interstitialoxygen occurs near the surface of the device substrate 100. In thepresent step, a width of the denuded zone 101 is determined by theannealing temperature and time. The width of the denuded zone 101 is10-50 μm in general.

The second heating treatment step is a cool-down step. A cool-down rateis 0.5-20° C./minute. A preferred cool-down rate is 3° C./minute. Atarget cool-down temperature is one temperature in a range of 500˜900°C. A preferred target temperature is 750° C. After the targettemperature is reached, an annealing time lasts for 0.5-64 hours. Apreferred time is 8 hours. An annealing atmosphere is an oxygen-freeatmosphere, and more particularly is N₂, Ar (or other inert gas), H₂, ormixture of the above-mentioned gases. In the present cool-down step, thenucleation of the saturated oxygen elements outside the denuded zone 101of the device substrate 100 occurs.

The third heating treatment step is a heat-up step. A heat-up rate is0.5-20° C./minute. A preferred heat-up rate is 3° C. /minute. A targettemperature is one temperature in a range of 900-1400° C. A preferredtarget temperature is 1150° C. After the target temperature is reached,an annealing time lasts for 0.5-40 hours. A preferred time is 16 hours.An annealing atmosphere is an oxygen-free atmosphere, and moreparticularly is N₂, Ar (or other inert gas), H₂, or mixture of theabove-mentioned gases. In the present step, the larger oxygenprecipitation is formed from the nucleation of the oxygen elementsoutside the denuded zone 101 of the device substrate 100, and meanwhilethe oxygen precipitation can effectively getter metal impurities in thedenuded zone 101.

In order to simplify the process for saving the annealing time, thepresent invention may implement only the first and second heatingtreatment steps. The third heat-up heating treatment step and thefollowing step of reinforcing the bonding interface may be integrated asone step for reducing the process complexity, saving the process costand increasing the process efficiency.

An implementation order of the above-mentioned steps S11 and S12 may bechangeable. An advantage of implementing step S11 first is that theinsulating layer 110 formed in advance can protect the surface of thedevice substrate 100 and reduce the time of the heating treatment,thereby decreasing the cost. When step S11 is implemented after step S12and the device substrate 100 is single crystal silicon, a cool-down stepmay be implemented in situ after the second heat-up step. A cool-downrate is 0.5-20° C./minute. A preferred cool-down rate is 3° C./minute. Atarget cool-down temperature is one temperature in a range of 900-1400°C. A preferred target temperature is 1050° C. After the cool-down step,in-situ oxidation process is implemented. An oxidation time isdetermined by a required thickness of an oxide layer. An oxidationatmosphere is a dry oxidation atmosphere, a wet oxidation atmosphere orAr/O₂ mixture. After the oxidation process, the oxide layer is formedand the oxide layer may be served as the insulating layer 110.

Referring to Step S13 as shown in FIG. 2D, the device substrate 100having the insulating layer 110 is bonded with the supporting substrate190, such that the insulating layer 110 is sandwiched between the devicesubstrate 100 and the supporting substrate 190.

When the supporting substrate 190 is a single crystal silicon substrate,preprocesses including a grinding process and a polishing process can bechosen to be performed on the single crystal silicon substrate 190before the bonding process, thereby thinning the thickness. Taking an8-inch single crystal silicon substrate for example, a thickness of thesubstrate is 750 μm, and a total thickness error of the substrate issmaller than 4 μm. A target thickness is 650 μm after thinning thesubstrate. Firstly, the single crystal silicon substrate is ground andthinned. A preferred grinding apparatus is a single-side grindingmachine. A device model of the grinding machine is DFG841. A coarsegrinding process is performed for achieving rapid thinning at a grindingwheel speed greater than 2000 rpm. Then, a fine grinding process isperformed at a grinding wheel speed greater than 2000 rpm for reducingdamage resulted from the coarse grinding process. After the grindingprocesses, the thickness of the substrate is greater than the targetthickness by at least 3 μm. Herein, the supporting substrate 190 isthinned to be 660 μm. A polishing process is performed on the groundsupporting substrate 190. The polishing process may be a single-sidepolishing process or a double-side polishing process, and it may be thedouble-side polishing process together with the single-side polishingprocess. Herein, the preferred polishing process is the double-sidepolishing process together with the single-side polishing process.Firstly, the double-side polishing process is performed. A device modelof a double-side polishing machine is Peter Wolters AC 2000. Thepolishing process is divided into two steps including a coarse polishingand then a fine polishing. A total polishing removal amount is 8 μm.Subsequently, the single-side polishing process is performed foraccurately controlling the thickness of the silicon wafer. A devicemodel of a single-side polishing machine is IPEC 372. The polishingprocess is also divided into two steps including a coarse polishing andthen a fine polishing. A polishing removal amount is not greater than 2μm. After the removal, an error of the total thickness of the substratecan be smaller than 1 μm.

Furthermore, it is optional to perform an insulating process on thesupporting substrate 190 before the bonding process, such that aninsulating and corrosion resistance layer covers the supportingsubstrate 190. More particularly, the corrosion resistance layer coversa back surface. A preferred insulating process may be a common oxidationprocess or a PECVD for depositing silicon dioxide, silicon nitride andso on. A thickness of the corrosion resistance layer is 1 μm in general.Since the following process is a reinforcing process at a lowtemperature, the supporting substrate 190 might not resist corrosion ofTMAH solution in the following chamfering process and many corrosionpits are formed on the back surface. Accordingly, the insulating andcorrosion resistance layer is formed in advance for protecting the backsurface of the supporting substrate.

After the preprocesses are performed on the supporting substrate 190, acleaning process and a bonding process are performed on the devicesubstrate 100 and the supporting substrate 190. The bonding process maybe a common hydrophilic bonding or a hydrophobic bonding, and it alsomay be a plasma assisted hydrophilic bonding. The hydrophilic bondingand the plasma assisted hydrophilic bonding are preferred. Taking thehydrophilic bonding for example herein, the substrates are cleaned byutilizing SC1 and SC2 solutions in sequence. Before the bonding process,a rotary cleaning process is performed on the device substrate 100 andthe supporting substrate 190 by a bonding machine EVG 801, therebyremoving particles which might exist on the surfaces and adsorbing morewater molecules. Then, the device substrate 100 is bonded with thesupporting substrate 190.

Referring to Step S14, an annealing and reinforcing process is performedon the bonding interface, such that an adherence level of the bondinginterface meets requirements in the following chamfering grinding,thinning and polishing processes. An annealing and reinforcingtemperature is 900° C.-1400° C. A preferred temperature is 1050° C. Anannealing and reinforcing time is 0.5-10 hours. A preferred time is 6hours. A heat-up rate is 0.5-20° C./minute. A preferred heat-up rate is3° C./minute. A preferred annealing atmosphere is a dry oxidationatmosphere or a wet oxidation atmosphere. When only the above-mentionedfirst and second heating treatment steps are performed, the present stepmakes the nucleation of the oxygen elements in the previous annealingstep at the low temperature form a larger oxygen precipitation, andmeanwhile the oxygen precipitation can getter metal impurities in thedenuded zone.

An additional reinforcing step is not required when the conditions inthe above-mentioned annealing and reinforcing process are utilized. Thatis, step S16 is not required. In order to avoid that the impuritiesdiffuse in the denuded zone 101 of the device substrate 100 in theannealing and reinforcing process, moderate conditions may be chosen inthe present step and then the additional reinforcing step is implementedin the following step S16. For example, an annealing and reinforcingtemperature is chosen at 500-1200° C., A preferred temperature is 900°C. A reinforcing time is 1-10 hours. A preferred time is 4 hours. Anannealing and reinforcing atmosphere is N₂, Ar (or other inert gas), O₂,N₂/O₂ mixture, Ar/O₂ mixture and so on. The above-mentioned moderateannealing conditions can have reinforcing effect on the bondinginterface for satisfying the requirements in the following chamferinggrinding, thinning and polishing processes.

Referring to Step S15 as shown in FIG. 2E, the chamfering grinding,thinning and polishing processes are performed on the bonded devicesubstrate 100. FIG. 2E shows a state after the above-mentioned processesare implemented. It is noted that controlling a removal amount in thethinning and polishing processes can ensure that the remained devicesubstrate 100 in FIG. 2E is totally composed of the denuded zone 101.

A chamfering process is performed on the device substrate 100 after thereinforcing process. A chamfering width is determined by specificationrequired by the following device processes. A thickness of a residuallayer in an edge after polishing is 0-150 μm. A preferred thickness is100 μm. The chamfered device substrate 100 is etched in TMAH solutionfor removing the residual layer in the edge by 100 μm. A preferredmethod is to spray THAH solution with a spin etching method. During theetching process, the substrate pair is rotated. A rotational speed is100-10000 rpm. A preferred rotational speed is 1000 rpm. A preferredtemperature of the THAM solution is 95° C. The reinforced devicesubstrate 100 is ground and thinned. A preferred grinding apparatus is asingle-side grinding machine. A device model of the grinding machine isDFG841. Firstly, a coarse grinding process is performed for achievingrapid thinning at a grinding wheel speed greater than 2000 rpm. Then, afine grinding process is performed for reducing damage resulted from thecoarse grinding process at a grinding wheel speed greater than 2000 rpm.After the grinding processes, the thickness of the device substrate 100should be greater than the target thickness of the device layer of thefinal product by at least 3 μm. Herein, the device substrate 100 isthinned to be 12 μm. A polishing process is performed on the grounddevice substrate 100. The polishing process may be a single-sidepolishing process or a double-side polishing process, and it may be thedouble-side polishing process together with the single-side polishingprocess. Herein, the preferred polishing process is the double-sidepolishing process together with the single-side polishing process.Firstly, the double-side polishing process is performed. A device modelof a double-side polishing machine is Peter Wolters AC 2000. Thepolishing process is divided into two steps including a coarse polishingand then a fine polishing. A total polishing removal amount is 4 μm.Subsequently, the single-side polishing process is performed foraccurately controlling the thickness of the silicon wafer. A devicemodel of a single-side polishing machine is IPEC 372. The polishingprocess is also divided into two steps including a coarse polishing andthen a fine polishing. A polishing removal amount is not greater than 2μm. After the polishing processes, the remained device substrate 100 istotally composed of the denuded zone 101.

In step S16, an additional annealing and reinforcing process isperformed on the bonding interface. When the moderate conditions of theannealing and reinforcing process in step S14 are utilized, the presentstep is required for enhancing a bonding strength between the supportingsubstrate 190 and the insulating layer 110 and forming covalent bonds inthe bonding interface. An annealing temperature in the present step is900-1400° C. A preferred annealing temperature is 1150° C. An annealingtime is 0.5-10 hours. A preferred time is 4 hours. A heat-up rate is0.5-20° C./minute. A preferred heat-up rate is 3° C./minute. A preferredannealing atmosphere is a dry oxidation atmosphere or a wet oxidationatmosphere. For the device substrate 100 made of the single crystalsilicon material, an oxide layer is further formed on the surface of thedevice substrate 100 during the oxidation process. The thickness of thedevice substrate 100 may be controlled by controlling the thickness ofthe oxide layer, thereby achieving an object of accurately controllingthe thickness of the device layer. After the annealing process, theoxide layer is removed by utilizing HF solution, and the final substratehaving a buried insulating layer is obtained. The device layer iscomposed of the denuded zone 101 of the device substrate 100.

An advantage of the above-mentioned technical scheme is that thegettering process is performed on the device substrate 100 beforebonding. The denuded zone 101 is formed on the surface, and then thedenuded zone 101 is transferred to the supporting substrate 190 forobtaining bonding material with high crystal quality. For furtherconsideration of thermal stability of the oxygen precipitation insidethe device substrate 100, two steps of annealing processes may be chosento be implemented in the preparing process. The first annealing step isa low-temperature annealing, such that the bonding strength meets therequirements in the grinding and polishing processes. Finally, thesecond step is utilized for reinforcing the bonding strength for formingcovalent bonds in the interface,

Furthermore, in the heating treatment process, only the first and secondheating treatment steps are performed on the device substrate 100, andthe third high-temperature heating treatment step and the subsequentstep of reinforcing the bonding interface are integrated as one step,thereby reducing the process complexity, saving the process cost andincreasing the process efficiency.

As is understood by a person skilled in the art, the foregoing preferredembodiments of the present invention are illustrative rather thanlimiting of the present invention. It is intended that they covervarious modifications and similar arrangements be included within thespirit and scope of the appended claims, the scope of which should beaccorded the broadest interpretation so as to encompass all suchmodifications and similar structure.

What is claimed is:
 1. A method for preparing a semiconductor substratewith a buried insulating layer by a gettering process, comprising thefollowing steps of: providing a device substrate and a supportingsubstrate; forming an insulating layer on a surface of the devicesubstrate; performing a heating treatment on the device substrate, so asto form a denuded zone on the surface of the device substrate; bondingthe device substrate having the insulating layer with the supportingsubstrate, such that the insulating layer is sandwiched between thedevice substrate and the supporting substrate; annealing and reinforcinga bonding interface, such that an adherence level of the bondinginterface meets requirements in the following chamfering grinding,thinning and polishing processes; and performing the chamferinggrinding, thinning and polishing processes on the device substrate whichis bonded.
 2. The method according to claim 1, wherein the devicesubstrate is a single crystal silicon substrate.
 3. The method accordingto claim 1, further comprising the following step of: performing anadditional annealing and reinforcing process on the bonding interfaceafter performing the chamfering grinding, thinning and polishingprocesses on the device substrate.
 4. The method according to claim 1,wherein the step of performing the heating treatment on the devicesubstrate further comprises: a first heating treatment step for forminga crystal zone on the surface of the device substrate; and a secondheating treatment step in which a temperature is lower than atemperature in the first heating treatment step, such that nucleation ofsaturated oxygen elements outside the denuded zone of the devicesubstrate occurs.
 5. The method according to claim 4, wherein the stepof performing the heating treatment on the device substrate furthercomprises: a third heating treatment step for making the nucleation ofthe oxygen elements in the second heating treatment step form a largeroxygen precipitation, and meanwhile the oxygen precipitation can gettermetal impurities in the denuded zone.
 6. The method according to claim1, further comprising the following step of: forming a protective layeron an exposed surface of the supporting substrate before performing thechamfering grinding, thinning and polishing processes on the devicesubstrate.